Abstract
Akirin is an essential nuclear protein involved in the regulation of NF-κB signaling pathway. In most invertebrates, Akirin regulates NF-κB-related Imd and Toll pathways, however, in Drosophila, it only controls the Imd pathway, whereas its role in NF-κB signaling pathway in other insect species is unclear. In the present study, we used white-backed planthopper Sogatella furcifera as a model to investigate the functional activity of Akirin in insects. The sequence of Akirin cDNA was extracted from transcriptome database of S. furcifera; it contained a 585 bp open reading frame (ORF) encoding a putative protein of 194 amino acids. S. furcifera Akirin (SfAkirin) had a molecular weight of about 21.69 kDa and a theoretical pI of 8.66 and included a nuclear localization signal (NLS) of five amino acid residues at the N-terminal region. Evolutionary analysis showed that SfAkirin was evolutionary closer to Akirins of such relatively distant species as crustaceans than to those of some insect orders like Diptera and Hymenoptera. Tissue-specific expression analysis showed that the SfAkirin gene was expressed in all examined tissues, with the highest expression levels detected in the testis, followed by the ovary, whereas the lowest expression was found in the head. Real-time quantitative PCR analysis showed that SfAkirin mRNA was strongly induced in response to injection of heat-inactivated Escherichia coli and Bacillus subtilis, whereas SfAkirin silencing by RNA interference significantly reduced the expression of NF-κB dependent transcription factors Dorsal and Relish after B. subtilis and E. coli challenge, respectively. Our results suggest that SfAkirin may control the immune response of S. furcifera against bacterial infection via both Imd and Toll signaling pathways.
Highlights
NF-κB is a nuclear transcription factor that activates the expression of genes involved in the immune response of insects to infections by pathogenic microorganisms and, plays a central role in the insect innate immunity (Hoffmann, 2003; Hultmark, 2003; Imler and Bulet, 2005)
SfAkirin was clustered with the proteins of the first insect group, and was evolutionary closer to Akirins of such relatively distant species as arachnids than to those of some insect orders like Diptera and Hymenoptera
In Drosophila, Akirin controls only the Imd pathway and is not involved in the regulation of the Toll pathway (Goto et al, 2008), which is in contrast to other invertebrates such as C. rogercresseyi and L. vannamei, where Akirin regulates both Imd and Toll pathways (Carpio et al, 2013; Hou et al, 2013)
Summary
NF-κB is a nuclear transcription factor that activates the expression of genes involved in the immune response of insects to infections by pathogenic microorganisms and, plays a central role in the insect innate immunity (Hoffmann, 2003; Hultmark, 2003; Imler and Bulet, 2005). There are three types of NF-κB transcription factors identified in insects: Dorsal, Dif, and Relish (Eleftherianos et al, 2013; Zhong et al, 2016), which participate in immunity-related Toll and Imd signaling pathways (Lemaitre et al, 1995; Valanne et al, 2011; Myllymaki et al, 2014). Dorsal and Dif are the downstream transcription factors involved in the Toll pathway which. The authors showed, for the first time, that the insect myeloid differentiation factor 2 (MD-2) could have a function similar to that of the mammalian MD-2 in immune signaling and expression control of antimicrobial peptides cathelicidins and proposed a Toll-LPS signaling pathway regulating immunity in insects
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